Gas lift is an artificial lifting method used to produce oil from wells that do not flow naturally. In gas-lifted wells, gas is injected through the well annulus and into the well tubing at a down-well location. The gas mixes with the oil in the tubing, aerating the oil and causing it to rise to the surface.
To pass through the annulus to the tubing, the injection gas flows through a valve commonly referred to as a gas lift valve. Gas lift valves comprise one-way valves that allow gas to pass from the annulus to the tubing yet prevents oil from passing from the tubing to the annulus. Many gas lift valves comprise a pressurized bellows valve and an internal check valve. The bellows valve opens when the injection gas is pressurized above a threshold value, and the internal check valve is used to prevent oil from passing through the gas valve from the tubing and into the annulus.
A gas lift valve can fail if it allows oil passage from the tubing to the annulus. For failure to occur, at least two conditions are simultaneously met: (1) the reverse-flow check valve has a leak and the tubing pressure exceeds the gas pressure; and (2) a combination of high tubing pressure and low gas pressure allows the bellows valve to open. Further, if both the check valve and the bellows valve leak, then backflow can occur any time the tubing pressure exceeds the annulus pressure. The proper function of gas lift valves is very important for the safety of the well and surface operations. For instance, if hydrocarbons improperly flow through the annulus and reach the wellhead, an undesired accumulation of high-pressure combustible material may occur at the well and surface and hence may increase the risk of injury to personnel and/or damage to equipment, as well as disruptions in operation.